Faulty generalization:

When a conclusion based on induction is unwarranted by the degree of relevant evidence or ignores information that warrants an exception.

He and his 4 brothers are bald, so his sister must also be bald.

Notes

This fallacy is common where there is a phase transition or physical threshold, or where there is something other than a linear relationship between elements.
A more detailed treatment of this fallacy can be found on the supplementary Inductive Errors page.

Case Study One

When conducting a survey of political opinions by calling cell phones, having an adequate sample size of millions will not rescue your survey from the methodological error of calling cell phones which the elderly and poor may not possess.

Case Study Two

A thousand successful walks across a frozen lake during sub-freezing temperatures does not warrant a generalization that it is safe to walk across on a warm day when the ice is thawing.